Ink jet printers are becoming an increasing popular type of device for recording permanent images on paper. Ink jet printers operate by directing a stream of minute ink droplets at the paper so as to produce a distinct pattern of individual ink dots. By selectively forming ink dots on paper, and by regulating the number of dots formed on the paper, an ink jet printer can be used to create almost any type of print: text; graphics; or images. This capability had made it attractive to attach ink jet printers to computer systems that produce both textual material and images simultaneously. This is because a properly programmed ink jet printer can be used to produce a complicated image and a detailed description of the image on the same page.
Moreover, many ink jet printers are capable of discharging multiple colors of ink so as to generate quality color figures and images. This capability has contributed to their popularity since computer systems that can generate multi-color video output in the form of graphics and images are becoming increasingly common. These computer systems require printing devices that can produce permanent images of the output they generate. The ability of ink jet printers to produce text and images in color has also made them useful for desk top publishing which allows a small user to efficiently, economically and rapidly produce publications that contain textual material that is accompanied by color images.
A popular type of ink jet printer is one that relies on solid ink that is melted immediately prior to jetting. These printers are often referred to as "hot-melt" ink jet printers and are said to rely on "phase-change" inks. Hot melt ink jet printers are used, in part, because the ink they discharge solidifies rapidly on contact with the paper and forms ink dots with very sharp optical edges so the resulting images are of very high quality. Phase change inks also have exceptional true color mixing properties which is an important characteristic for color printers that typically have three base color inks, plus black ink, that are blended together to print a very large spectrum of intermediate colors.
A typical hot melt ink jet printer has an ink jet reservoir, in communication with a set of one or more ink jets, for each color of ink jetted therefrom. The ink jet reservoirs have heating elements and are adapted to receive ink in either a solid or liquid state and melt and/or maintain the ink in the liquid state prior to jetting. The ink jets are in communication with the reservoirs and are designed to jet onto the paper liquid state ink jetted therefrom. If the printer is a multi-color printer it uses a number of reservoirs, at least one for each color of ink jetted therefrom. Separate ink jets are connected to each of the reservoirs to jet the ink therein.
An important consideration in the design of hot-melt ink jet printers is providing a means to supply solid ink for melting and subsequent jetting. One concern in the design of a solid ink delivery system is the need to limit the amount of solid ink delivered for melting at any one time. If too much ink is delivered for melting, liquefied ink may flow out of the reservoir and onto the printer, possibly damaging the ink supply delivery system, or another element of the printer.
Moreover, if there is excessive ink in the reservoir it may inhibit the shutting down and starting up of the ink jet printer such as at the end and beginning of successive days of operation. For instance, if there is a large amount of ink in the reservoir at the end of the day, it will all resolidify when the printer is turned off at the end of the day and the heating elements are deactivated. At the start of the next day, the printer is turned on, it may take a considerable amount of time to reliquefy all the ink in the reservoir so the printer is ready for printing. This would delay the start of the printing when the printer is first turned on.
Furthermore, the repeated melting, resolidification, and subsequent reliquefaction of some inks may change their chemical properties in a way that would adversely affect how they are jetted by the printer or appear on the paper after jetting.
Another reason excessive amounts of solid ink should not be supplied for melting is that it is undesirable to maintain phase change ink in the liquid state for an excessive amount of time prior to jetting. This is because the heat supplied to maintain the ink in the liquid state may also "cook" desirable volatile components out of the ink. The volatile components may be ones that inhibit the ink from developing solid deposits, or clotting, as it is supplied through the jets. The volatile components may also contribute the ink's desirable optical qualities when it is jetted onto the paper.
Another consideration is providing enough solid ink for liquefaction and jetting. If insufficient amounts of liquid ink are in a reservoir, the ink jets connected thereto may not be able to maintain a sufficient head of ink to continually jet ink when they are activated. If the ink jets are unable to jet ink regularly, the subsequent images produced by the printer would be significantly degraded.
Still another factor in supplying solid ink, or any ink, to an ink jet printer involves color printers and the need to insure that the right color ink is supplied to each reservoir and associated jets. If the wrong color ink is supplied to a reservoir and subsequently jetted, the image produced will be wholly undesirable. Moreover, the cost and time required to clean the reservoir and jets so the proper color ink can be loaded therein would be quite high.
Printer mechanical error can cause the wrong color ink to be supplied to a hot melt ink jet printer. Mechanical error is possible because the printing system of most hot melt ink jet printers are designed to move across the paper being printed on so substantially all of it may be printed on. Consequently, there is always the possibility the ink reservoirs and the ink supply system will be out of registration, and the wrong color ink will be supplied to a reservoir.
Furthermore, the ink supply means should be designed so as to minimize the number and unpleasantness of the tasks the operator tending to the printer has to perform. Thus the ink should be packaged in a form that is not undesirable for the operator to handle. Moreover, the operator should be able to supply the printer with a large amount of ink so he/she does not use excessive amounts of time refilling it with same.
There have been some attempts at providing solid ink supply systems wherein the solid ink is contained as a cartridge that is coupled to the reservoir. The ink cartridge is heated an ink dripped into the reservoir below. A disadvantage of this system is that either excessive ink or not enough ink may be supplied to the reservoir. Also, the ink cartridges contain only a limited amount of ink. If the ink jet printer the ink cartridges are part of is used a lot, the operator may have to spend an excessive amount of time replacing empty cartridges. Moreover providing ink in cartridges tends to be relatively expensive.